This invention relates to shutters for use in cameras, and more particularly, to electromagnetically operated slit exposure shutters.
Many camera shutters use a spring as the power source for the shutter and energize or cock the spring in connection with the operation of the camera's film transport mechanism. This arrangement has made it difficult to facilitate minimizing the bulk and size of the camera and to practice low cost production techniques.
Recently, proposals have been made for using an electromagnetic force for driving shutter blades through an exposure operation. A wide variety of electromagnetically operated shutters are being considered. This type of shutter has the advantage of simplicity because it does not need the aforementioned complicated mechanisms. However, the usual cameras suitable for employing such shutters require small and light drive sources and batteries. Therefore, small capacity batteries should normally be selected for this purpose. However, this limits the output of the electromagnetic drive device. It makes it difficult for the shutter blades to achieve sufficiently high operating speeds.
In general, inner magnet-type electromagnetic drive sources are suitable for incorporation into cameras of this type. In such devices, however, it is difficult to insure uniform magnetic flux distribution over the entire working range of the moving coil, and the drive torque exerted varies with the positions along the drive path.
Generally, the drive torque at the start of a shutter blade run is inadequate. This, along with the inertia and friction of the shutter blades, results in a loss of acceleration that prevents uniform exposure over the entire area of the film format.
An object of the present invention is to eliminate the aforementioned disadvantages.
Another object of the invention is to improve electromagnetically operated shutters.
Another object of the invention is to provide electromagnetically operated shutters which can start at high speeds.